The invention relates to the field of thin film magnetic transducers (heads) and to methods for fabricating thin film magnetic transducer with recessed magnetic elements.
A typical prior art disk drive system 10 is illustrated in FIG. 1. In operation the magnetic transducer 11, usually called a xe2x80x9cheadxe2x80x9d is attached to an arm or actuator 13 and flies above the rotating disk 16. A voice coil motor (VCM) (not shown) pivots the actuator 13 to position the magnetic transducer 11 over selected circumferential tracks on the disk 16. The disk 16 is attached to spindle 18 that is rotated by a spindle motor 24. The disk 16 comprises a substrate 26 on which the magnetic medium 21 is deposited. The magnetic medium 21 is used to record the magnetic transitions written by the magnetic transducer 11 in which information is encoded. A tape based storage system uses a magnetic transducer in essentially the same way as a disk drive, with the moving tape being used in place of the rotating disk 16.
The magnetic transducer 11 is composed of elements that perform the task of writing magnetic transitions (the write head 23) and reading the magnetic transitions (the read head 12) as illustrated in the merged head shown in FIG. 2. The electrical signals to and from the read and write heads 12, 23 travel along conductive paths (leads) (not shown) which are attached to or embedded in the actuator 13. Typically there are two leads each for the read and write heads 12, 23.
FIG. 2 is a midline section perpendicular to the air bearing surface of one type of prior art magnetic transducer 11 for use in a disk drive 10. The components of the read head 12 are the first shield (S1), two insulation layers 107, 109 which surround the magnetoresistive sensor element 105 and the second shield 104 (P1/S2). The sensor element 105 may include multiple layers of material in addition to the magnetoresistive material as is the case in a spin valve sensor. This type of magnetic transducer 11 is called a xe2x80x9cmerged headxe2x80x9d because the P1/S2 layer 104 serves as a shield for the read head 12 and a pole piece for the write head 23. The yoke also includes a second pole piece 103 (P2) which connects with P1/S2104 at the xe2x80x9cback gapxe2x80x9d (BG). The P2103 confronts the P1104 across the write gap layer 42 to form the write gap 43 at the air bearing surface (ABS). The coil 37 in this particular prior art head is deposited on a layer of resist 106 which is used to define the zero throat height (ZTH) by forming a step on the gap layer 42. FIG. 3 is symbolic illustration of a prior art tape storage system 203 which utilizes a tape cartridge 202. The tape storage system 203 uses a magnetic transducer assembly 211 which is positioned between fixed tape support pins 228, 229. The electrical signals to and from the magnetic transducer assembly 211 are processed by channel electronics 231. The tape cartridge 202 includes reels 220, 221 on which magnetic tape 222 is stored. The magnetic tape 222 is supported by pins 225, 227. In operation the magnetic tape 222 is positioned in contact or near contact to magnetic transducer assembly 211 as the tape is moved in either direction to and from reels 220, 221. The magnetic transducer assembly 211 indudes a plurality of magnetic transducers to read and write multiple tracks across the width of the tape simultaneously. Separate magnetic transducers are used for each track.
FIG. 4 is a midline section illustrating of a type of prior art magnetic transducer assembly 211 used in tape storage systems. The transducer assembly 211 includes symmetrical components which allow simultaneous reading and writing. These are illustrated as left transducer 51A with its closure pieces 71A and right transducer 51B with its closure pieces 71B. The tape 222 moves from left to right as well as right to left. The left transducer 51A and right transducer 51B are respectively included in the left module 53A and the right module 53B which are supported by the left u-beam 55A and the right u-beam 55B.
FIG. 5 is a section of a transducer 51 such as might be used for the left and/or right transducers 51A, 51B. The relative sizes are not shown to scale, since the wide range of sizes would make the drawing unclear. The section is taken parallel to the tape bearing surface (not shown). The substrate 61 supports undercoat 63 which is an insulating material such as alumina. The first shield (S1) 65 is a magnetically permeable material such as Sendust which has been used in tape heads for many years and is well known in the art. Sendust is a nonductile material. The magnetoresistive sensor element 67 is separated from S165 by the first gap 66. The second gap 68 separates the magnetoresistive sensor element 67 from the second shield 69. The magnetoresistive sensor element 67 may be a single layer or multiple layers. The first and second gaps 66, 68 are typically alumina, as is the overcoat 70. The second shield 69 may be a ferromagnetic material such as permalloy (80 at. % nickel, 20 at. % iron) which is ductile. The closure piece 71 is placed on top of the overcoat 70.
FIG. 6 is a section of the prior art transducer 51 taken perpendicular to the tape bearing surface 72. The prior art lapping process results in the tape bearing surface 72 being substantially planar around the magnetoresistive sensor element 67 with each of the components being essentially flush with the tape bearing surface 72. A problem with prior art heads which results from the action of the moving magnetic media is that elements such as the magnetoresistive sensor element 67 and the second shield 69 which are made from ductile material can be mechanically distorted by having the surface material pushed and pulled into a nonplanar, drift-like shape.
Thin film deposition processes used to fabricate heads typically create a film which conforms to the surface topography on which it is being deposited. When the thin film structures of differing materials are etched, the resulting surface may be significantly nonplanar. The deposition of a subsequent conformal film leaves the surface in a nonplanar state. A planarization process which is commonly used in both thin film head and semiconductor fabrication is called chemical-mechanical polishing (CMP). Both acidic and basic solutions have been suggested for use in CMP to speed up the rate of material removal. The prior art of fabricating magnetic transducers (heads) has included lapping the surface of the heads to present a smooth surface to the magnetic media. The lapping process is performed on rows of heads which have been cut from the wafer after all of the thin film structures have been formed. Lapping the heads is typically a mechanical process, but use of a slurry with an alkaline pH is suggested by Brar, et al., in U.S. Pat. No. 4,837,923. The purpose is to add an etching action in addition the mechanical abrasion. A pH of nine is said to be preferable. The result is claimed by Brar, et al., to be a smooth surface with the pole tip exposed and flush with the surrounding material.
Applicant discloses a novel magnetic transducer which has selected elements recessed from the surface of the transducer. The magnetic sensor element is recessed below its surrounding gap material and the second shield (S2) is preferably recessed below the level of the gap material. The magnetic sensorelement and the second shield are typically made from ductile material. Recessing the softer and more ductile elements below the surrounding ceramic material, results in superior resistance to physical distortion resulting from the action of the moving magnetic media. Applicant discloses two methods for producing magnetic transducers with recessed elements according to the invention. One method uses a lapping medium which chemically etches the selected material more aggressively than the surrounding material resulting in the selected material being recessed from the surface of the transducer. Since lapping is typically already performed as a part of the fabrication process, no additional process steps are required by this method. For transducers in which the magnetic sensor element and the second (S2) are made from alloys of nickel and iron, an acidic lapping medium is preferred to achieve the desired structure. A second method for fabricating the transducer structure according to the invention uses sputter-etching. When the thin film structure for the magnetic transducer is subjected to the working gas atoms in a sputtering chamber, the magnetic material sputter-etches more rapidly than the surrounding ceramic material resulting in the magnetic material being recessed from the surface of the transducer. The sputter etching is performed after the conventional lapping process and before or after the individual transducers are sliced from the rows.
Heads according to the invention are preferably used in tape drive systems, but use in disk storage systems is feasible.